This invention relates generally to the field of variable geometry turbochargers and, more particularly, to an actuator crank arm that is used to operate a unison ring and that is specially configured to have a reduced contact stress, when compared to convention actuator crank arm designs, thereby providing improved operational efficiency and lengthened service reliability.
Turbochargers for gasoline and diesel internal combustion engines are devices known in the art that are used for pressurizing or boosting the intake air stream, routed to a combustion chamber of the engine, by using the heat and volumetric flow of exhaust gas exiting the engine. Specifically, the exhaust gas exiting the engine is routed into a turbine housing of a turbocharger in a manner that causes an exhaust gas-driven turbine to spin within the housing. The exhaust gas-driven turbine is mounted onto one end of a shaft that is common to a radial air compressor mounted onto an opposite end of the shaft and housed in a compressor housing. Thus, rotary action of the turbine also causes the air compressor to spin within a compressor housing of the turbocharger that is separate from the turbine housing. The spinning action of the air compressor causes intake air to enter the compressor housing and be pressurized or boosted a desired amount before it is mixed with fuel and combusted within the engine combustion chamber.
In a turbocharger it is often desirable to control the flow of exhaust gas to the turbine to improve the efficiency or operational range of the turbocharger. Variable geometry turbochargers have been configured to address this need. A type of such variable geometry turbocharger is one having a variable exhaust nozzle, referred to as a variable nozzle turbocharger. Different configurations of variable nozzles have been employed in variable nozzle turbochargers to control the exhaust gas flow. One approach taken to achieve exhaust gas flow control in such variable nozzle turbochargers involves the use of multiple pivoting vanes that are positioned annularly around the turbine inlet.
In previous embodiments of variable nozzle turbochargers such as that disclosed in U.S. patent application Ser. No.: 09/408,694 entitled xe2x80x9cVariable Geometry Turbochargerxe2x80x9d, now U.S. Pat. No. 6,269,642, having a common assignee with the present application, the pivoting vanes are commonly controlled by a unison ring that is positioned within the turbine housing. The unison ring is operated to vary the pitch of the multiple pivoting vanes by an actuator shaft that extends from a turbocharger center housing into the turbine housing. An actuator crank arm is attached at the end of the shaft and includes an outwardly projecting pin that registers with a slot in the unison ring. The unison ring is rotated to open or close the plurality of vanes by rotation of the crank arm and movement of the pin within the slot. It is known that this pin-in-slot cooperating interaction between the actuator crank and the unison ring places a large degree of contact stress on the pin and arm during operation. The large degree of contact stress is known to cause binding and other undesired effects that impair the efficient and reliable operation of the unison ring.
It is, therefore, desired that an actuator crank arm and unison ring be configured in a manner such that the connecting mechanism between the two provide a reduced amount of contact stress on one or both of the members, when compared to the conventional design. This improved connecting mechanism is desired for purposes of increasing operational efficiency and extending service reliability, and ultimately the service life of a turbocharger comprising the same.